The present invention is a class of coated particles (powders) where the coating is multifunctional and is distinguished from previous inventions in that it contains UVB, UVA, and visible light absorbers as well as stabilizers integrally grafted into the coating. The coating also contains elements which enhance the dispersion of the particles into common fluids and resins to support high solids loadings. In another aspect of this invention, the coating can impart photostability (substantial reduction of photoreactivity) in the cases where the base particles are light absorbers themselves.
The coated particles of the present invention are suitable for use in any particle-loaded system where light absorption is desired (e.g. photo-protection applications), but have particular utility in topical sunscreen applications. The most advantageous molecules to be integrally grafted into the coating are thought to be common organic UVB absorbers, UVA absorbers and light stabilizers commonly employed in topical sunscreen applications.
A notable deficiency of organic UVB absorbers, UVA absorbers and light stabilizers used in sunscreen is absorption through the skin, which is associated with these species being small molecules. A number of studies have now shown that such organic UV filters can be absorbed through the skin after topical application where they may be metabolized, excreted, or bioaccumulated. Following absorption into the skin, the presence of these molecules may have deleterious effects caused by the generation of free radicals (genotoxicity) or may also be associated with the endocrine disruption. This information is discussed in detail A. Chisvert et al. Analytica Chimica Acta 752, 11-29 (2012).
One of the advantages of the present invention is that it allows for the efficient protective action of organic UV filters and stabilizers while preventing them from absorbing into the skin since they are anchored to a particle via incorporation into the coating. It has now been demonstrated in several studies that particles, even nanoparticles, do not penetrate human skin and that the stratum corneum is an effective barrier to penetration. See V. R. Leite-Silva et al. European Journal of Pharmaceutics and Biopharmaceutics 104, 140-147 (2016); A. M. Holmes et al. ACS Nano 10, 1810-1819 (2016); and Australia TGA 2016 Literature Review on the safety of titanium dioxide and zinc oxide nanoparticles in sunscreens. 
A further aspect of this invention takes advantage of substantial reduction in photoreactivity that the coating imparts to the coated base particle in the case where the particle is a light absorber (wide band gap semiconductor). This is accomplished by suppression of free radical species that are normally generated following photo-excitation of a wide band gap semiconductor particle. The suppression (quenching) of these free radical species prevents the free radical attack on susceptible species, such as antioxidants, that would normally follow light absorption. This absence of photo-generated radicals as well as the photo-protective action of the coated powder of the present invention on antioxidant molecules, in effect, boosts the activity of these species by preventing their degradation or deactivation.
The invention claims the compositions of the coated powders, solid and liquid dispersions incorporating the coated particles (powders), sunscreen and cosmetic formulations incorporating the coated particles (powders), method of protecting human skin and keratinous materials through the use of the coated particles, method of protecting photosensitive active ingredients (antioxidants) through the use of the coated particles, and the skin health benefits associated with enhancing the activity of photosensitive active ingredients (antioxidants).
It should be noted that while the compositions of the present invention have not been synthesized to date, methods of synthesizing said compositions are described in detail below employing well-known chemical synthetic routes that would be understood by one of ordinary skill in the art.